FIELD OF THE INVENTION
This invention relates to a non-aqueous liquid system comprising a dispersion of polymers in a non-aqueous liquid.
A non-aqueous liquid dispersion of polymers is useful as a paint, ink, adhesive and the like, and it has advantages in that the amount of solvent used in the paint can be reduced and it can be a photochemically non-active solvent.
One of the known methods for producing a non-aqueous system liquid dispersion of polymers comprises subjecting vinyl-type monomers, the polymers of which are insoluble in an organic liquid, to graft polymerization in the presence of a dispersion stabilizer which is soluble in said organic liquid. Many methods are known which employ many combinations of a dispersion stabilizer and a vinyl-type monomer.
For example, as a dispersion stabilizer, there are mentioned a decomposed rubber in U.S. Pat. No. 3,257,340, butylated melamine--formaldehyde resin in U.S. Pat. No. 3,365,414, self-condensates of 12--12--stearate--glycidyl methacrylate--methyl methacrylate--copolymer in U.S. Pat. No. 3,514,500, and glycidyl methacrylate-alkyl methacrylate-acrylic acid--copolymer (Japanese Laid-Open Publication No. SHO50-126093 (1975)).
These methods have faults in that the processes not only are complicated, but also, because the polymerization yield thereof in the graft polymerization process is low, the reaction time thereof is long and the productivity is low and the dispersion stability of the liquid dispersion is bad (the duration of stable storage is about one month).
As another method for producing a non-aqueous system comprising a liquid dispersion of polymers, Japanese Patent Laid-Open Publication No. SHO49-5194 (1974) proposes to produce the same by a process comprising carrying out a two-step polymerization in an organic liquid, using peroxyester-type peroxides having two peroxy bonds whose decomposition temperatures are different from each other, wherein the first step comprises polymerizing a vinyl-type monomer or mixture thereof in the organic liquid at a temperature corresponding to the lower decomposition temperature of the peroxide, thereby obtaining a polymer which is soluble in the organic liquid, and the second step comprises subjecting the product of the first step and another vinyl-type monomer to graft polymerization, at a temperature corresponding to the higher decomposition temperature of the peroxide thereby to obtain a polymer which is insoluble in the organic liquid.
This method has faults in that about half of the polymers produced by the first step are polymers which do not take part in the second step, because the peroxides used are the peroxyester type peroxide having two peroxy bonds. Accordingly the graft efficiency is low and the resulting liquid dispersion is poor in dispersion stability.